1. Field of the Invention
The present invention relates to an industrial furnace, a burner thereof and a combustion method therefor for conducting regenerative combustion. In regenerative combustion, heat from exhaust gas is stored in a heat storage member by causing exhaust gas to flow through the heat storage member. Gas flow through the heat storage member is then alternately switched between supply air flow and exhaust gas flow, whereby supply air flowing through the heat storage member, in which the heat from the exhaust gas is stored, is heated by the heat storage member.
2. Description of Related Art
Japanese Patent Publication No. HEI 5-246423 discloses a pair of burners for conducting regenerative combustion which are alternately switched in operation. A heat storage member is mounted in a main body of each burner, and a switching valve is disposed outside the main body of each burner in communication with the main body of each burner.
As a result, the burner has a problem that piping for connecting the switching valve and the main body of the burner needs to be provided. This makes the combustion apparatus large. Therefore, a long purging time period at every switching time results because the volume in the piping to be purged is large.
To address such problems, one of the applicants of the present application proposed a burner for conducting regenerative combustion wherein a switching mechanism is mounted within a main body of the burner. In the burner, a heat storage member is sectioned into a plurality of circumferential sections by partitioning plates extending in an axial direction of the burner. A rotatable disk slidably contacts end surfaces of the partitioning plates so that supply air flow and exhaust gas flow through the sections of the heat storage member are switched in accordance with rotation of the rotatable disk.
Further, with the proposed burner, as well as the burner of Japanese Patent Publication No. HEI 5-256423, a fuel release surface and an air supply and gas exhaust surface, where a plurality gas flow holes for causing supply air and exhaust gas to pass therethrough are open, are positioned in the same plane perpendicular to an axis of the burner.
However, the proposed burner and the burner of HEI 5-256423 still have the following problems:
First, because the same gas flow hole is used as a supply air flow hole and as an exhaust gas flow hole by switching a gas flow between supply and exhaust, a cross-sectional area for allowing supply air to pass therethrough and a cross-sectional area for allowing exhaust gas to pass therethrough are equal with each other. As a result, it is difficult to raise a supply air flow speed by throttling the cross-sectional area of the supply air flow hole, because if throttled, the cross-sectional area of the exhaust gas flow hole is necessarily also throttled, which raises the internal pressure of the furnace to an intolerable level. Thus, the supply air flow speed cannot be raised. As a result, the amount of burnt gas drawn and involved by the supply air flow and recirculated in the furnace is small, making it difficult to suppress generation of NOx. Further, the amount of fuel drawn by the supply air flow is also small, which degrades combustion and shortens the length of a combustion zone in a direction from the burner toward an opposite end of the furnace.
Second, supply air is likely to leak through a clearance between the end surfaces of the partitioning plates and the rotatable disk, shortening the path to the exhaust gas. As a result, the supply air flow speed is further decreased, which strengthens the above problems. Further, the shortened path will cause a deficit in available supply air, thereby causing imperfect combustion and increasing CO in the exhaust gas.
Third, when combustion is conducted using the conventional burner having the fuel release surface and the air supply and gas exhaust surface in the same plane, amount of CO (carbon monoxide) and NOx (nitrogen oxides) in the exhaust gas is large, so that some treatment for decreasing the amount of CO and NOx is often needed. Further, the combustion zone produced by the conventional burner is usually short.